Pineal Gland

They've switched the pineal gland in older mouse to that of a young mice and the older mice have lived better and gotten younger (I'm not sure how beneficial the effect was I'd like to know) theoretically you could do that in humans, it would just be dangerous?

How much did the pineal gland of the younger mouse regenerate the older mouse?

You do realize that the donor is left without a pineal gland, right? You already have asked enough questions about transplants and transfusions to understand the rejection issue for humans (mice bred in the lab are very similar genetically, so do not have as much of a problem with this as humans would), and if you stop to think about where the donor tissue comes from, you'd also realize this is a highly unethical thing to even consider. Lastly, take a look at a picture of where the pineal gland is located, and you'll get the last clue of why this is a ridiculous proposal.